1. Field of the Invention
This invention relates to a heated fuser roller as is commonly used in copying machines, and more particularly to a heated fuser roller having multiple groupings of internal heat elements.
2. Description of the Prior Art
A typical approach to fusing a toner image is by a hot roller-pressure fuser apparatus. In this type of apparatus, the paper, with the toner image thereon, is passed between a pair of rollers, at least one of which is heated. Generally, the heated roller formed of a hollow cylinder having a radiant heater, such as an infrared lamp, centrally located within the cylinder, to heat the roller. During operation of the fusing apparatus, the paper to which the toner image is electrostatically adhered is passed through a nip, formed between the rollers, with the toner image contacting the fuser roller to effect heating of the toner image within the nip. A thermostat, monitoring the process, intermittently interrupts or restores the current flow, to the infrared lamp, in an attempt to maintain the surface roller temperature at a predetermined optimum value.
Many of the problems that occur with the use of the hot roller-pressure fusing apparatus relate to the means employed for heating the fuser roller and its control. For example, in many of the known hot roller fusers it is extremely difficult to maintain a desired temperature, at particular sections of the roller, along the nip where the actual fusing of the toner occurs, and where temperature control is critical. Temperature control is difficult because (1) paper of different sizes requires enlarging or decreasing the heating zone, of the roller, to conform to the size of the paper; (2) neither a single central element nor multiple heating elements, such as disclosed in U.S. Pat. Nos. 4,266,115, 4,377,366 and 4,585,325, is able to adjust to all the varying demands of non-uniform thermal output during the fusing process; and (3) adjustments must be made for different machine modes, i.e., standby, off, continuous operation.